Examination of the putative Ca2+-binding site in the light-harvesting complex 1 of thermophilic purple sulfur bacterium Thermochromatium tepidum

Long Jiang Yu, Shogo Kato, Zheng Yu Wang

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The core light-harvesting complex (LH1) of purple sulfur photosynthetic bacterium Thermochromatium tepidum exhibits an unusual absorption maximum at 915 nm for the Qy transition, and is highly stable when copurified with reaction center (RC) in a LH1-RC complex form. In previous studies, we demonstrated that the calcium ions are involved in both the large red shift and the enhanced thermal stability, and possible Ca2+-binding sites were proposed. In this study, we further examine the putative binding sites in the LH1 polypeptides using purified chromatophores. Incubation of the chromatophores in the presence of EDTA revealed no substantial change in the absorption maximum of LH1 Qy transition, whereas further addition of detergents to the chromatophores-EDTA solution resulted in a blue-shift for the LH1 Q y peak with the final position at 892 nm. The change of the LH1 Qy peak to shorter wavelengths was relatively slow compared to that of the purified LH1-RC complex. The blue-shifted LH1 Qy transition in chromatophores can be restored to its original position by addition of Ca 2+ ions. The results suggest that the Ca2+-binding site is exposed on the inner surface of chromatophores, corresponding to the C-terminal region of LH1. An Asp-rich fragment in the LH1 α-polypeptide is considered to form a crucial part of the binding network. The slow response of LH1 Qy transition upon exposure to EDTA is discussed in terms of the membrane environment in the chromatophores.

Original languageEnglish
Pages (from-to)215-220
Number of pages6
JournalPhotosynthesis research
Volume106
Issue number3
DOIs
Publication statusPublished - Oct 1 2010

Keywords

  • Energy transfer
  • Membrane protein
  • Photosynthesis
  • Sulfur bacteria

ASJC Scopus subject areas

  • Biochemistry
  • Plant Science
  • Cell Biology

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